Methods and apparatus for removing solids from a membrane module

ABSTRACT

A method of operating a membrane filtration module, the module including one or more membranes extending longitudinally between vertically spaced upper and lower headers into which the ends of the membranes are potted. The membranes have a permeable wall which is subjected to a filtration operation wherein feed containing contaminant matter is applied to one side of the membrane wall and filtrate is withdrawn from the other side of the membrane wall. At least one of the upper and/or lower headers has one or more openings therein and the method including flowing the feed, at least in part, through the one or more openings for application to the membrane wall. Apparatus for performing the method is also disclosed.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §120 as a division of U.S. application Ser. No. 11/575,234 filed on Mar. 14, 2007, titled METHODS AND APPARATUS FOR REMOVING SOLIDS FROM A MEMBRANE MODULE, which is a U.S. national stage application that claims priority under 35 U.S.C. §371 to International Application No. PCT/AU05/01396 filed on Sep. 13, 2005, titled METHODS AND APPARATUS FOR REMOVING SOLIDS FROM A MEMBRANE MODULE, that claims priority to Australian Provisional Application Ser. No. 2004905292, titled METHODS AND APPARATUS FOR REMOVING SOLIDS FROM A MEMBRANE MODULE, filed Sep. 14, 2004, each of which is herein incorporated by reference in their entirety for all purposes.

TECHNICAL FIELD

The present disclosure relates to membrane filtration systems and, more particularly, to a method and apparatus for improving the filtration efficiency of such systems by providing an improved cleaning system for the membranes.

BACKGROUND

In a membrane filtration process, the method used to physically clean membranes is of vital importance. An efficient membrane cleaning strategy can maintain a stable permeability of the membrane and reduce the frequency of chemical cleans. A commonly used method to physically clean membranes is a backwash (also called “backflush” or “backpulse”) with the permeate/filtrate or a gas. The backwash method is typically used to eject solids blocking the membrane pores and partly dislodge the cake that may have formed on the membrane surface. In a system exposed to a feed containing a high concentration of solids, the fouling occurs more quickly and more severely, in particular, where membranes are densely packed in a module.

Backwash with pressurized gas has proved a very efficient cleaning method and is now widely used in the field of microfiltration processes. The limitation to this method is the membrane pore size. Backwash of membranes with permeate has no limitations to the pore size, but the backwash efficiency is generally lower than gas backwash and the transmembrane pressure (TMP) recovery is not enough to offset the fouling rate. Further means are employed to enhance the backwash efficiency, such as dosing chemicals to the backwash permeate, or in combination with gas scrubbing.

Maruyama et al. in Japanese Patent No. JP2031200 discloses a hollow fiber membrane backwashing method. The method involves the following sequence: stop filtration, air-scour membrane, fill the membrane vessel, backwash with permeate under pressurized air, and drain the waste. This procedure is repeated to achieve a higher efficiency. Sunaoka et al. in U.S. Pat. No. 5,209,852 describes a process for scrubbing hollow fiber membranes in modules. This process is composed of a two-stage air scrubbing and draining to clean the membranes.

In order to minimize footprint and cost, membrane modules are typically manufactured with a high packing density of membranes, usually in the form of fibers. This increases the amount of membrane area for filtration within a module. However, the higher the packing density, the more difficult it is to effectively flush solids captured during the filtration process from the membrane bundle. Therefore, improvement in the efficiency of solids removal during backwash allows either higher solids levels to be processed or higher membrane packing densities to be used, reducing the cost of treatment.

In prior art fiber membrane systems, removal of solids is usually effected by sweeping with feedwater from one end of the module to the other and then out of the module through a side exit port. In this case, solids are first swept along the fibers to the exit end of the module, but must then cross the fiber bundle to exit the module. In many applications this requirement for the flow to change direction and pass perpendicular to the fiber bundle to exit the module can lead to accumulation of solids near the exit due to the tendency for the fibers to act like a string filter and capture or hinder the exit of solids from the module at this point.

SUMMARY

In accordance with one or more embodiments, a membrane filtration module is provided, comprising one or more filtration membranes located in a vessel and extending longitudinally between vertically spaced upper headers and lower headers into which the ends of the one or more filtration membranes are potted, at least one of the upper and the lower headers having one or more openings defined therein, and an open-ended plenum chamber positioned at a base of the membrane filtration module below the lower header and having an open lower end spaced from a port in the base of the vessel without any intervening structures therebetween, wherein the one or more openings of the at least one of the upper and the lower headers, the open lower end of the open-ended plenum chamber, and the port in the base of the vessel are vertically aligned to the one or more longitudinally extending filtration membranes.

According to another embodiment, the one or more openings are provided in the lower header and the membrane filtration module further comprises a permeate chamber in fluid communication with the upper header. In various embodiments, the one or more openings in the lower header, the open lower end of the open-ended plenum chamber, and the port in the base of the vessel are configured to define an uninterrupted flow path for dislodged contaminant matter to exit the membrane filtration module in a direction substantially parallel to the one or more filtration membranes. In certain embodiments, the membrane filtration module further comprises a source of pressure configured to apply pressure to a feed liquid within the module. In some embodiments, the membrane filtration module further comprises a source of backwash fluid in fluid communication with the permeate chamber. In various embodiments, the membrane filtration module further comprises a gas supply manifold configured to supply a gas to the one or more openings in the lower header. In at least one aspect, the gas supply manifold is positioned adjacent the one or more filtration membranes and is further configured to direct gas downward into the open-ended plenum chamber. In one or more aspects, the gas supply manifold includes a port vertically aligned to the open lower end of the open-ended plenum chamber and the port in the base of the vessel. In certain embodiments, the port is positioned below the one or more openings in the lower header. According to some embodiments, the vessel is open to atmosphere.

According to one or more embodiments, a membrane filtration system is provided, comprising a plurality of filtration modules located in a vessel, each of the plurality of filtration modules including one or more membranes having permeable walls and extending longitudinally between vertically spaced upper headers and lower headers into which the ends of the one or more membranes are potted, the lower headers having one or more openings defined therein, a single open-ended plenum chamber in fluid communication with the one or more openings in the lower headers and having an open lower end spaced from a port in the base of the vessel without any intervening structures therebetween, and a gas supply manifold disposed between the plurality of filtration modules and configured to direct gas downward into the single open-ended plenum chamber between the plurality of filtration modules.

In various embodiments, the one or more openings in the lower headers, the open lower end of the single open-ended plenum chamber, and the port in the base of the vessel are vertically aligned to the one or more longitudinally extending filtration membranes. In another aspect, the one or more openings in the lower headers, the open lower end of the single open-ended plenum chamber, and the port in the base of the vessel are configured to define an uninterrupted flow path for dislodged contaminant matter to exit the membrane filtration system in a direction substantially parallel to the one or more membranes. In at least one embodiment, the membrane filtration system further comprises a source of pressure configured to apply pressure to a feed liquid in the plurality of filtration modules. In certain embodiments, the membrane filtration system further comprises at least one permeate chamber in fluid communication with the upper headers. In some embodiments, the membrane filtration system further comprises a source of backwash fluid in fluid communication with the at least one permeate chamber. In various aspects, the gas supply manifold includes a port vertically aligned to the open lower end of the single open-ended plenum chamber and the port in the base of the vessel. In some aspects, the port is positioned below the one or more openings in the lower headers.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 shows a schematic sectional view of a membrane module according to one embodiment;

FIG. 2 shows a schematic sectional view of a membrane module according to further embodiment; and

FIGS. 3 a and 3 b show an enlarged schematic sectional view of the lower header of a non-pressurized filtration system during the aeration and drain-down phases, respectively.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the FIG. 1, the filtration module 5 is mounted within a housing vessel 6 which contains the feed to be filtered. The filtration module 5 contains a bundle or bundles of hollow fiber membranes 7 extending between upper and lower headers 8 and 9, respectively. The lower header 9 is provided with a number of openings 10 communicating with the interior of the fiber bundle and an open-ended plenum chamber 11 having an opening 11′. An inlet/outlet port 12 is provided at the base of the module 5. Feed is supplied through ports 12, 13 and 14 under the control of valves AV5, AV1 and AV2.

Permeate/filtrate is withdrawn through chamber 15 and port 16 under control of valve AV3. A backwash may also be applied through port 16 under the control of valve AV4.

FIG. 2 shows a similar arrangement to FIG. 1; however, in this embodiment the hollow fiber membranes 7 are suspended vertically from the upper header 8 and are not potted at their lower distal ends 19. The distal ends 19 of each fiber membrane 7 are closed and filtrate withdrawn through the upper header 8.

In use, solids accumulated within the modules 5 following filtration and backwash are flushed or swept from the modules 5 through the openings 10 by opening port 12 and applying a suitable pressure to the feed within the module 5. The waste is flushed through the opening 11′ in the plenum chamber 11 and removed through open port 12.

FIGS. 3 a and 3 b show an enlarged view of the lower headers 9 of a pair of modules 5 connected to a single plenum chamber 11 in a non-pressurized filtration system. The modules 5 in this embodiment are mounted in an open vessel (not shown) and the waste liquid containing solids accumulated within the modules 5 following filtration and backwash is drained through the openings 10 under force of gravity, as shown in FIG. 3 b.

As best shown in FIG. 3 a, port 17 connected to a gas supply manifold 18 may also be used to supply gas to openings 10 to provide scouring bubbles within the module 5 to assist cleaning of the fiber membrane surfaces.

Systems embodying the disclosure may provide a number of benefits including:

1. Enhanced solids removal during backwash due to sweeping action along the fiber surface rather than across multiple fibers.

2. Easier contact of feed liquid with the inside of the membrane bundle during filtration (feed liquid can be drawn into the centre of the bundle through the same holes during filtration). This also induces a form of crossflow during filtration.

3. Rack inserts containing sets of membrane modules can be lowered down closer to the bottom of the module as an open area is no longer required beneath the modules to accommodate manifolds and piping used for solids removal and feed inlet, this now takes place through the openings in the pot. The result is better void space reduction efficiency as well as less space for drainage.

4. The plenum chambers can be connected to a pipe or manifold and the backwash waste pumped out of the module rather than gravity flowed, and/or the feedwater pumped in during filtration.

It will be appreciated that further embodiments and exemplifications of the disclosure are possible with departing from the spirit or scope of the disclosure described. 

What is claimed is:
 1. A membrane filtration module comprising: one or more filtration membranes located in a vessel and extending longitudinally between vertically spaced upper headers and lower headers into which the ends of the one or more filtration membranes are potted, at least one of the upper and the lower headers having one or more openings defined therein; and an open-ended plenum chamber positioned at a base of the membrane filtration module below the lower header and having an open lower end spaced from a port in the base of the vessel without any intervening structures therebetween, wherein the one or more openings of the at least one of the upper and the lower headers, the open lower end of the open-ended plenum chamber, and the port in the base of the vessel are vertically aligned to the one or more longitudinally extending filtration membranes.
 2. The membrane filtration module of claim 1, wherein the one or more openings are provided in the lower header and the membrane filtration module further comprises a permeate chamber in fluid communication with the upper header.
 3. The membrane filtration module of claim 2, wherein the one or more openings in the lower header, the open lower end of the open-ended plenum chamber, and the port in the base of the vessel are configured to define an uninterrupted flow path for dislodged contaminant matter to exit the membrane filtration module in a direction substantially parallel to the one or more filtration membranes.
 4. The membrane filtration module of claim 3, further comprising a source of pressure configured to apply pressure to a feed liquid within the module.
 5. The membrane filtration module of claim 2, further comprising a source of backwash fluid in fluid communication with the permeate chamber.
 6. The membrane filtration module of claim 2, further comprising a gas supply manifold configured to supply a gas to the one or more openings in the lower header.
 7. The membrane filtration module of claim 5, wherein the gas supply manifold is positioned adjacent the one or more filtration membranes and is further configured to direct gas downward into the open-ended plenum chamber.
 8. The membrane filtration module of claim 7, wherein the gas supply manifold includes a port vertically aligned to the open lower end of the open-ended plenum chamber and the port in the base of the vessel.
 9. The membrane filtration of claim 8, wherein the port is positioned below the one or more openings in the lower header.
 10. The membrane filtration module of claim 1, wherein the vessel is open to atmosphere.
 11. A membrane filtration system, comprising: a plurality of filtration modules located in a vessel, each of the plurality of filtration modules including one or more membranes having permeable walls and extending longitudinally between vertically spaced upper headers and lower headers into which the ends of the one or more membranes are potted, the lower headers having one or more openings defined therein; a single open-ended plenum chamber in fluid communication with the one or more openings in the lower headers and having an open lower end spaced from a port in the base of the vessel without any intervening structures therebetween; and a gas supply manifold disposed between the plurality of filtration modules and configured to direct gas downward into the single open-ended plenum chamber between the plurality of filtration modules.
 12. The membrane filtration system of claim 11, wherein the one or more openings in the lower headers, the open lower end of the single open-ended plenum chamber, and the port in the base of the vessel are vertically aligned to the one or more longitudinally extending filtration membranes.
 13. The membrane filtration module of claim 12, wherein the one or more openings in the lower headers, the open lower end of the single open-ended plenum chamber, and the port in the base of the vessel are configured to define an uninterrupted flow path for dislodged contaminant matter to exit the membrane filtration system in a direction substantially parallel to the one or more membranes.
 14. The membrane filtration system of claim 13, further comprising a source of pressure configured to apply pressure to a feed liquid in the plurality of filtration modules.
 15. The membrane filtration system of claim 11, further comprising at least one permeate chamber in fluid communication with the upper headers.
 16. The membrane filtration system of claim 15, further comprising a source of backwash fluid in fluid communication with the at least one permeate chamber.
 17. The membrane filtration system of claim 11, wherein the gas supply manifold includes a port vertically aligned to the open lower end of the single open-ended plenum chamber and the port in the base of the vessel.
 18. The membrane filtration module of claim 17, wherein the port is positioned below the one or more openings in the lower headers.
 19. The membrane filtration system of claim 11, wherein the vessel is open to atmosphere. 